Apparatus for making a multi-layered blown plastic container

ABSTRACT

A multi-layered blown plastic container is formed by injection molding a first thermoplastic parison, axially stretching the first parison at its orientation temperature, injection molding a second thermoplastic parison around the first parison, and blowing the multi-layered parison at its orientation temperature to provide an oriented container, the inner layer being oriented in the axial and hoop directions, and the outer layer oriented in the hoop direction.

This is a Division of application Ser. No. 303,759 filed Sept. 21, 1981now U.S. Pat. No. 4,364,896.

THE INVENTION

The present invention is directed to a method and apparatus for makingan oriented hollow blown plastic container. The invention is moreparticularly related to a method of making a multi-layered holloworiented plastic container.

It is an object of the present invention to provide a method of making amulti-layered hollow blown plastic container comprising the steps of:

(A) injection molding a first parison of thermoplastic material,

(B) axially stretching the parison at its orientation temperature toprovide a parison that is oriented in the axial direction,

(C) injection molding at least a second thermoplastic parison around thestretched first parison to form a multi-layered parison,

(D) bringing the multi-layered parison to orientation temperature; and

(E) blowing the multi-layered parison to form a multi-layered orientedhollow plastic container in which the inner layer is oriented in theaxial direction and the hoop direction, and the outer layer is orientedin the hoop direction.

It is an object of the present invention to provide a multi-layeredoriented hollow plastic container in which the inner layer is made ofpolyethylene terephthalate and is oriented in the axial direction andthe hoop direction, and the outer layer is made of polyvinylidenechloride and is oriented in the hoop direction.

These and other objects will become apparent from the specification andclaims that follow and the drawings in which:

FIG. 1 is a diagrammatic top plan view illustrating the method of thepresent invention and the four station blow molding machine of thepresent invention, with some parts being shown in section;

FIG. 2 is a schematic top plan view of the second station showing thefirst injection molded parison in section;

FIG. 3 is a schematic top plan view of the second station showing thestretched first injection molded parison in section; and

FIG. 4 is a schematic top plan view of the second station showing twolayer parison in section.

The present invention provides a method and apparatus for making amulti-layered oriented hollow plastic container, the method comprisingthe steps of:

(A) injection molding a first parison of thermoplastic material such aspolyethylene terephthalate,

(B) axially stretching the parison at orientation temperature to provideaxial orientation to the parison,

(C) injection molding at least a second thermoplastic parison of athermoplastic such as polyvinylidene chloride around a stretched firstparison to form a multi-layered parison,

(D) bringing the multi-layered parison to orientation temperature; and

(E) blowing the multi-layered parison to form a multi-layered orientedhollow plastic container in which the first layer is oriented in theaxial direction and the hoop direction and the outer layer is orientedin the hoop direction.

The present invention also provides an apparatus for blow molding anoriented multi-layered hollow plastic container comprising:

(A) a first station having injection molding means for providing a firstthermoplastic parison,

(B) a second station having means for stretching the first parisonaxially and a second injection molding means for injection molding asecond thermoplastic parison around the first stretched parison toprovide a two-layer parison,

(C) a third station for blow molding the two-layer parison at itsorientation temperature, and

(D) a fourth station for ejecting the finished blown container.

The blow molding apparatus of the present invention as shown in FIG. 1comprises a first station 10 having injection molding means 12 includingan extruder nozzle 13 and a channel 14 for providing a firstthermoplastic parison 15 such as one of substantially amorphouspolyethylene terephthalate in a mold 16. The apparatus comprisespreferably a horizontal indexing turret head 20 which indexes to threeother stations after the first station 10. The apparatus can also be onethat operates in a vertical plane.

As best seen in FIG. 1, a second station 30 is provided which has meansfor stretching the first parison axially 40 to form a stretched parison45 and a second injection molding means 50 for injection molding asecond thermoplastic parison 60 such as one of polyvinylidene chloridearound the first stretched parison 45 to provide a two-layered parison70.

A third station 80 is provided for blow molding the two-layered parisonat its orientation temperature in a blow mold 82 to provide a finaloriented hollow plastic container 75, having an inner layer 76 that isoriented in the axial direction and the hoop direction and an outerlayer 77 that is oriented in the hoop direction, as is well known in theart, Blow air can conveniently be supplied to the interior of theparison through an axial air passage inside the core pin.

A fourth station 81 is provided for ejecting the finished blowncontainer 75. In the method and apparatus of the present invention, acore pin 90, upon which the parisons travel throughout the indexingoperation, is a combination of a core pin to carry the parisonsthroughout, a stretch pin (as seen in Station 2), and a blow pin (asseen in Station 3). The combination core pin, stretch pin and blow pincan be seen in detail on an enlarged scale as in FIGS. 2, 3, and 4.

In Station 2, the first injection molded parison is carried from Station1 by the core pin 90 to a mold 95. In Station 2 (as best seen in FIG. 3)the core pin is moved axially to stretch the parison to form a stretchedparison. As seen in FIGS. 1 and 3, a hydraulic activated cylinder or rod99 moves within the cylindrical bore 100 to stretch the first parison atits orientation temperature to provide the stretched parison.Thereafter, still at Station 2, a parison is injection molded around thefirst stretched parison to provide a two-layered parison as seen in FIG.4. Then as previously explained, the stretched parison is blown atStation 3 to form the two-layered oriented hollow plastic article 75 andindexed to Station 4 where the hollow plastic bottle is ejected, thecore pin moving away from the bottom of the container whereby the bottledrops from the pin by gravity.

The two-layered parison is generally of such a size that its wallthickness is about 60 to 180 mils, especially when the final containerhas a volume of about 1 to 2 liters or more, up to as high as 3 to 4liters. The wall thickness of each of the layers of the two-layeredparison is such that each layer is preferably about 40-60% of the totalthickness and generally about 30-70% of the total thickness.

The final container is generally such that the wall thickness is about 8to 30 mils for containers ranging from about one-half liter up to about2 to 3 liters. The preferred material for one of the layers such as theinner layer or first injection mold parison is polyethyleneterephthalate (PET) with an inherent viscosity of about 0.6 to 1.1 . Theorientation temperature of PET, as is known in the art, is about70°-110° C. for best results. The orientation temperature ofthermoplastic materials is generally well known, and the orientationtemperature for orienting the first injection mold parison by axiallystretching should be somewhere in the middle of its orientation rangefor best practical results. As to the orientation temperature forblowing the final two-layered parison to form a blown container,inasmuch as the orientation temperatures of each of the differentpolymers vary somewhat, the temperature should be an average orientationtemperature for the two materials so that both layers can becomeoriented in the hoop direction.

Thermoplastic polymers suitable for use in the present invention,especially for the first injection molded parison, are polyethylene,polypropylene, polyvinyl chloride, nitrile polymers, polyethyleneterephthalate, polycarbonate, polymethyl methacrylate, and nylon.Suitable polymers for the second injection molded parison, although theycan also be used as the first injection molded parison, include goodbarrier polymers such as polyvinylidene chloride. The barrier polymersare less permeable to CO₂ and O₂ than the other polymers. For instancepolyvinylidene chloride much less permeable to CO₂ and O₂ than ispolyethylene or polypropylene. Other polymers that can be included as abarrier layer include co-polymers of vinylidene chloride with vinylchloride or vinyl alcohol or vinyl acetate or styrene. Polyvinyl alcoholor polyvinyl acetate and co-polymers of vinyl alcohol and vinyl acetatecan be used. A suitable polymer is a hydrolyzed ehtylene vinyl acetateco-polymer. Also co-polymers of vinylidene chloride and acrylonitrilecan be used.

The amount of stretching of the parison in the axial direction atStation 2 is preferably at least about 40% of its length, and bestresults are obtained with about 50-150% or more of its original length.In other words, the parison can be stretched (100%) to double its lengthfor good results. As illustrated in FIGS. 2 and 3, when the firstinjection molded parison is stretched axially to about double itslength, the wall thickness of the stretched parison is reduced to aboutone half of its original wall thickness.

A great advantage is obtained by having different oriented layers. Bythe method of the present invention, the layers can be oriented at adifferent time in the process and the orientation can be in differentdirections.

What is claimed is:
 1. An apparatus for blow molding an orientedmulti-layered hollow plastic container comprising:A. a first stationhaving pin means including a core pin and having injection molding meansfor forming a first thermoplastic parison about the core pin, B. asecond station including the pin means in which the core pin serves as astretch pin for stretching the first parison axially and a secondinjection molding means for injection molding a second thermoplasticparison around the first stretched parison on the stretch pin to providea two-layer parison, C. a third station including means for blow moldingthe two-layer parison at its orientation temperature to form a blowncontainer, the pin means being a blow pin at the third station; and D. afourth station including means for ejecting the finished blowncontainer, the pin means being so constructed and arranged that the corepin transports the first parison, the stretched two-layer parison, andthe blown container to the second, third and fourth stations.
 2. Theapparatus as defined in claim 1 in which the first parison, thetwo-layered parison and the blown container are transported to theirrespective stations by the pin means, the pin means being so constructedand arranged that the pin means serves as a core pin at the firststation and transports the parison to second station, the pin meansserving as a stretch pin at the second station and transports thetwo-layered parison to the third station, the pin means serving as ablow pin at the third station and transports the blown container to thefourth station.